1. Field of the Invention
The present invention relates to interference cancellation in a wireless communication system. More particularly the present invention relates to an apparatus and a method for removing interference in a Multiple Input Multiple Output (MIMO) wireless communication system.
2. Description of the Related Art
A High Speed Packet Access (HPSA) system of the 3rd Generation Partnership Project (3GPP) uses a 2×2 MIMO system of simultaneously transmitting a High-Order Modulation (HOM) of a 64-Quadrature Amplitude Modulation (QAM) and two streams.
An HSPA system uses a data channel (HS-PDSCH) having a smaller Spreading Factor (SF) in comparison with a Wideband Code Division Multiple Access (WCDMA) mobile communication system. Inter-Symbol Interference (ISI) or Inter-Cell Interference (ICI) may be efficiently suppressed for symbols having a large SF through de-spreading by a receiver. However, in a symbol having an SF of 16, it has become difficult to protect the symbol with only de-spreading. Accordingly, instead of a RAKE reception method, which has been generally used, a method of estimating a transmission signal with an equalizer is used.
While an equalizer has an advantage in that the equalizer can effectively invert a channel matrix, the equalizer also has a disadvantage in that reliability of the estimated transmission signal is lowered due to deterioration of the inversion performance when an interference signal is high. For this reason, it has become an important research issue for increasing the reception performance that equalization is performed while an interference signal is properly processed. In a CDMA system or a MIMO system using interference cancellation, technologies for performing a signal detection with the interference cancellation have been conventionally researched, but the technologies are not suitable for being applied to an HSPA system having frequency selective fading, so that an equalizer for interference cancellation is required.